1. Field of the Invention
The present invention relates to a vehicle lighting device with a reflector having a transmissive member.
2. Related Art
In vehicle lighting devices, light emitted from a light source on an optical axis extending in front and rear direction is reflected toward a front side by a reflector. Disclosed in JP-A-05-120903 is a reflector having a transmissive member.
In a vehicle lighting device disclosed in JP-A-05-120903, an exterior surface of the reflector of the transmissive member is formed with a plurality of total reflection prisms so that light emitted from a light source is reflected toward a front side of the lighting device by using the total reflection in each of the total reflection prisms.
In addition, discloses in U.S. Pat. No. 4,839,781 is a reflector made of a transmissive member having an exterior surface formed with a plurality of protruding portions extending in a radial pattern with respect to an optical axis and each of the protruding portions has a total reflection prism of which a cross section belonging to a plane perpendicular to the optical axis is set to have approximately a V shape, even though the device disclosed in U.S. Pat. No. 4,839,781 is not a vehicle lighting device.
As disclosed in JP-A-05-120903 and U.S. Pat. No. 4,839,781, in the case in which the reflector is made of the transmissive member and the exterior surface of the reflector is formed with a plurality of total reflection prisms, it is possible to omit a process of forming a mirror surface on the reflector, which allows a cost of manufacturing a lighting device to be saved.
In this case, by constructing such that a vehicle lighting device includes the reflector as disclosed in U.S. Pat. No. 4,839,781, it is possible to realize the total reflection on the exterior surface over almost an entire region of the reflector and to make the direction of the totally reflected light approximately parallel to the direction of light reflected from an interior surface. Accordingly, most of the light beams emitted from a light source can be effectively used as illumination light emitted toward the front side of the lighting device.
However, since the exterior surface of the reflector disclosed in U.S. Pat. No. 4,839,781 is formed with the plurality of protruding portions extending in a radial pattern with respect to an optical axis, the light distribution pattern formed by the light reflected from the reflector becomes a circular light distribution pattern, which causes a problem in that it is not possible to form a horizontally long light distribution pattern that the vehicle lighting device is supposed to form.
In this case, for some of the plurality of protruding portions, by properly changing the angle of inclination of a pair of inclined surfaces forming the protruding portion, it is possible to make the light reflected from a corresponding protruding portion slightly diffused in the direction of a tangential line of the circumference with respect to the optical axis. However, at this time, when the angle of inclination changes largely, the total reflection at the protruding portion cannot be maintained. For this reason, from the view point of an effective use of light beams emitted from a light source, the allowable variation amount of the angle of inclination of each inclined surface is extremely small. Accordingly, even though it is possible to slightly change the shape of the circular light distribution pattern by using the construction described above, the problem in which the horizontally long light distribution pattern cannot be formed still occurs.